Toxoplasma gondii is a frequent cause of disease in humans and animals. It is very often a cause of central nervous system infection in patients with the acquired immune deficiency syndrome (up to 25%), causes retinitis and blindness in children and adults and congenital toxoplasmosis and death in children and mothers infected during pregnancy. In some areas of the world (e.g., Asia) over 90% of the population may be infected with 3-4% with retinal involvement and visual loss. Control of the disease in humans will require development of a vaccine either for humans or for the animals from which humans predominantly acquire this disease (i.e., cats, pigs). Development of live, attenuated, or killed vaccines for pathogens are dependent upon development of large scale production techniques for growth of these organisms. T. gondii is normally grown by intraperitoneal inoculation of mice. This is far too expensive a technique to grow large numbers of organisms and also requires the use of laboratory animals. While T. gondii has been isolated from specimens in fibroblast cell lines, these cell lines grow in adherent monolayers and therefore do not allow accumulation of large parasite densities. No large scale production technique for growth of tachyzoites, the tissue destructive form of T. gondii, has been performed as yet.
In the patent literature, there are several references which disclose immunization procedures involving Toxoplasma gondii. In U.S. Pat. No. 4,473,549 (Frenkel et al.), a method is disclosed for immunizing man and animals against toxoplasmosis which involves production and subcutaneous administration of a live, low-virulent form of T. gondii. U.S. Pat. No. 4,473,548 (Frenkel et al.) discloses a method of immunizing cats against shedding of Toxoplasma oocytes which involves treatment with an agent such as monensin or salinomycin which prevents such shedding while allowing immunization to the parasite. U.S. Pat. No. 4,480,043 (Trouyez) discloses a process for preparing toxoplasmas to be used for the diagnosis of toxoplasmosis involving inoculation of mice with a mixture of toxoplasmas and sarcomatous cells. Finally, U.S. Pat. No. 4,564,592 (Gaafar et al.) discloses production of a "Toxoplasma factor" believed to be responsible for pathologic conditions observed in toxoplasmosis. This patent discloses producing this toxofactor by injecting T. gondii intraperitoneally in mice, and subsequently recovering the factor, which is usable in vaccines, from the culture medium. None of these patents disclose a method for generating large-scale production of Toxoplasma parasites for use in vaccines and antibody detection.